1. Field of the Invention
The invention generally relates to a magnetic recording and/or reproducing apparatus for use with a magnetic disk cartridge. More particularly, the invention relates to apparatus that provides a stable, i.e., substantially constant, transducer-to-disk relation for enhancing the recording or reproducing of information signals on a flexible magnetic disk.
2. Description of the Prior Art
For successfully recording or reproducing information signals on a magnetic disk, particularly at high densities, there should be little or no spacing between the transducer and the disk. In addition, it is preferred that such transducer-to-disk relation remain substantially constant over a wide range of operating parameters. Unfortunately, especially with a magnetic disk that is flexible, as for example a floppy disk, the transducer-to-disk relation may be varied by the interaction of many parameters, such as temperature, humidity, relative speed between the disk and the transducer, contour of the transducer, penetration (dimpling) of the transducer into the disk, flexibility and variations in thickness of the disk, etc.
To ensure a substantially constant spacing between a flexible magnetic disk and a magnetic head, it has been proposed, as in U.S. Pat. No. 3,178,719, that the magnetic disk be rotated in close proximity to an annular stabilizing plate, sometimes referred to as a Bernoulli plate, which causes the rotating disk to assume a stable position at a small distance from the stabilizing plate. A plurality of magnetic heads, radially disposed with respect to the flexible disk, are embedded in the stabilizing plate, either slightly above or slightly below (e.g., 0.002") or flush with the top surface of the plate facing the disk. Presumably, the top surface of the plate and the magnetic heads are relatively arranged to allow the heads to penetrate into the flexible disk as the disk is rotated. Since the close spacing between the stabilizing plate and the rotated disk, and therefore the critical spacing between the magnetic heads and the rotated disk, varies as a function of the disk radius, a vacuum pump is included to create a partial vacuum in respective openings around each one of the heads. The partial vacuum deforms small areas of the flexible disk around the magnetic heads to independently control the close spacing between each one of the heads and localized portions of the disk.
Although the apparatus disclosed in U.S. Pat. No. 3,178,719 may perform satisfactorily, it requires the use of a vacuum pump to control the critical head-to-disk spacing, which increases the construction and operating costs of such apparatus. A simpler apparatus that dispenses with the need for a vacuum pump is disclosed in U.S. Pat. No. 4,074,330. In that apparatus, a stabilizing (Bernoulli type) plate has a groove which is sealed at its ends, is open to a flexible disk, and is radially disposed with respect to the disk. A magnetic head, movable along the groove, projects from the groove to penetrate into the flexible disk. Bracketing the groove, on either side of the head, is a pair of up-stream and down-stream air bearing arcuate surfaces which are radially coextensive with the groove. The respective apexes of the two air bearing surfaces are located closer to the top surface of the stabilizing plate facing the flexible disk, than to the radially extending sides of the groove. With this arrangement, it is purported that the amount of air carried by the rotated disk out of the groove is greater than the amount of air carried by such disk into the groove. The net result is to exhaust air from the groove, which generates a Bernoulli pull down force on the rotated disk over the groove. Such pull down force is opposite to the tendency of the rotated disk to dimple away from the magnetic head because of penetration of the head into the disk, and therefore ensures a stable close spacing between the head and the disk.
When a magnetic disk is housed permanently in a cartridge, the stability of the head-to-disk relation may be affected by certain surfaces of the cartridge proximate the rotated disk. One approach for ensuring a stable head-to-disk relation in a disk cartridge is disclosed in U.K. Patent Application GB No. 2,101,391A, published Jan. 12, 1983 and in IEEE Transactions on Consumer Electronics, Vol. CE-28, No. 3, August 1982, p. 326. In that example, the disk cartridge includes an opposed pair of openings which extend radially on either side of the magnetic disk. As the flexible disk is rotated, a magnetic head is moved along one of the openings, in the nominal plane of revolution of the disk, to penetrate the disk and a guide plate in the other opening limits the tendency of the rotated disk to lift off the magnetic head. Use of the guide plate reduces the head-to-disk spacing to about 0.07 microns. Without the guide plate, the head-to-disk relation may vary to the extent that the signal-to-noise ratio will be unacceptable.